Preformed tray comprising ultra low density polyethylene

ABSTRACT

A customized dental tray comprising ULDPE is formed using a person&#39;s own teeth as a template, or using a stone model of the person&#39;s teeth. A preformed dental tray or sheet comprising ULDPE is heated to become plastically deformable and placed over at least a portion of the person&#39;s teeth in order to form an impression of the person&#39;s teeth and yield an intermediate customized dental tray. Upon cooling sufficiently, the intermediate tray is removed from the persons&#39; mouth and trimmed as needed to yield a finished customized tray corresponding to the person&#39;s teeth. The performed tray or sheet preferably comprises ULDPE, which yields a highly flexible and resilient final tray, although they may also contain other polymers or blends. The customized dental tray is useful for teeth bleaching and other dental treatments known in the art.

BACKGROUND OF THE INVENTION

[0001] 1. The Field of the Invention

[0002] The present invention is in the field of customized dental traysused to provide a desired dental treatment to a person's teeth. Moreparticularly, the invention relates to customized dental trays that areformed using either a person's teeth or a stone model of the person'steeth as a template. The tray can be used for dental treatments such asbleaching, administration of fluoride, or application of othermedicines.

[0003] 2. The Relevant Technology

[0004] Virtually all people desire white or whiter teeth. To achievethis goal, people either have veneers placed over their teeth or havetheir teeth chemically bleached. In the past, patients who desired tohave their teeth bleached had to submit to conventional in-officebleaching techniques. The process generally involves: (1) making analginate impression of the patient's teeth; (2) making a stone cast ormodel of the impression; (3) vacuum forming a dental tray from themodel, usually from a sheet of thin ethyl vinyl acetate (EVA) material,and trimming to exclude gingival coverage. This method results in a traythat is soft and flexible, that is very accurately customized to thepatient's teeth, but the method is time consuming and the resulting trayis expensive.

[0005] Because of the high cost of these very accurate custom trays,less costly alternatives have been developed, but these alternativeshave substantial disadvantages in terms of accuracy and comfort of thefinished formed tray.

[0006] One alternative is the so-called “boil and bite” tray. Arelatively thick, non-custom preformed tray (similar to a mouth guard)made of EVA or polyethylene or other material is submerged in boilingwater. Upon removal from the water, the tray is quickly placed insidethe patient's mouth. The patient quickly applies contact pressure tomake an impression of the biting surfaces of the user's teeth. Oneproblem with “boil and bite” trays is that they are relatively thick andbulky, which make them intrusive and uncomfortable to wear. Thethickness of large, bulky perform trays also limits the accuracy withwhich they can conform to the user's teeth and/or gums.

[0007] To the extent that preform trays made from EVA and like materialsare made with thinner walls, such trays are extremely difficult to workwith because they tend to shrivel and collapse outside extremely narrowwindows of temperature and heating time. For example, if left in a hotwater bath too long (i.e., for more than a few seconds) they can quicklybecome limp and lose their pre-form shape, making it difficult orimpossible to make an impression of the user's teeth. In view of theforegoing, “boil and bite” trays that do not have the tendency tocollapse and shrivel when heated generally do not accurately conform tothe user's teeth and are bulky and uncomfortable to wear.

[0008] Another alternative for teeth bleaching involves non-customizedstrips of a flexible plastic material coated with a bleaching agent thatcan be applied to the teeth. Such strips are placed against the teeth bythe user to cover the teeth. Because such strips are flimsy and limp atroom temperature (i.e., are not resilient or rigid), they are not usefulfor creating a customized dental tray.

[0009] Another alternative is a dual tray assembly as disclosed in U.S.Pat. No. 5,616,027 to Jacobs et al. The dual tray assembly is composedof an outer tray that supports or carries an inner tray made of athermoplastic material comprising EVA. In use, the tray assembly issubmerged in hot water, where the inner tray becomes pliable andmoldable and the outer tray remains rigid. “Because of the material andthe thinness of the walls of the inner tray, the inner tray willsubstantially lose integrity of its shape and form during the heatingprocess . . . .” (Col. 4, ll. 14-16.) Thus, “[t]he carrier tray isnecessary during the heating, handling and forming process.” (Col. 4,ll. 16-17.) The heated assembly is then placed in the mouth of thepatient where the inner tray takes an impression of the person's teeth.The generally thinner inner tray results in a final tray that is muchthinner and more comfortable to wear compared to conventional “boil andbite” trays that are sufficiently thick that they do not need asupporting carrier tray. Nevertheless, the outer tray can inhibitaccurate conformation of the inner tray to the shape of the patient'steeth.

[0010] Another problem with EVA are concerns about its toxicity. Whereastrays made using EVA are generally safe to use, the FDA has guidelinesthat strictly controls how EVA can be used. Notwithstanding theforegoing deficiencies, EVA finds wide use in the manufacture of dentaltrays, which is strong evidence of the inadequacy of other possibleplastic materials that are suggested in various existing patentsrelating to tray technology. EVA is generally preferred due to itssoftness and flexibility and the ease in which it can be heated andformed into a dental tray compared to other plastic materials suggestedin the art.

[0011] In view of the foregoing, there is an ongoing need to develop newmaterials for use in manufacturing preformed trays and sheets that canbe easily formed into customized trays that are thin-walled, flexible,comfortable, and that accurately reflect the shape of the person'steeth.

SUMMARY OF THE INVENTION

[0012] The present invention is directed to customized dental trays thatin one aspect are formed by using a person's own teeth as a template. Inthis case, a preformed tray or sheet is heated to a point where it issufficiently softened that it can be plastically molded so as to conformto the person's teeth. Upon cooling, the customized tray retains itsshape so that it can be used repeatedly as needed to provide a dentaltreatment. In another aspect, preformed trays or sheets comprising ultralow density polyethylene are formed into customized trays using a stoneor plaster model of the person's teeth.

[0013] The process for making a finished customized tray begins with apreformed dental tray or flat sheet that may optionally be available inmultiple sizes to allow the selection of a size that generally conformsto the size of the person's teeth and mouth. The tray or sheetpreferably comprises ultra low density polyethylene (“ULDPE”), eitheralone or blended with one or more additional polymers, e.g.,ethylene-vinyl acetate copolymer (“EVA”), ε-polycaprolactone (“PCL”),other types of polyethylene (“PE”), polypropylene (“PE”), or otherplastic materials. Plasticizers or flow additives known in thethermoplastic art can be used as desired to modify the properties of thethermoplastic material used to form the preformed dental tray or sheet.

[0014] Preformed trays and sheets made from ULDPE are preferred due tothe unique ability of trays and sheets made therefrom to soften and yetmaintain their physical integrity while in a softened state compared toprevious tray or sheet materials such as EVA. Thus, ULDPE expands theoperational window, both in terms of temperature and heating time, ofmanufacturing customized dental trays compared to previous traymaterials. In other words, preformed trays and sheets made from ULDPEare far less susceptible to over or under heating compared to trays orsheets made from EVA. Even though preformed trays and sheets made fromULDPE do not shrink or otherwise lose their physical integrity whenheated as happens using trays or sheets made from EVA, they do, in fact,shrink over and around and cling to the person's teeth (or a stone castof the person's teeth) when cooling, which greatly simplifies andimproves the ability of such trays or sheets to accurately conform tothe person's teeth (or stone cast). Moreover, ULDPE is non-toxic,thereby addressing any potential concerns with the toxicity of EVA,while providing the aforementioned superior physical and/or mechanicalproperties. These demonstrate the surprising and unexpected benefits ofusing preformed trays or sheets comprising ULDPE compared to traysmaterials considered at present to be the industry standard (i.e., trayscomprising EVA).

[0015] The outer configuration of the preformed dental tray ispreferably a horseshoe shape, with a flat planar bottom having an openU-shaped cross-section to generally fit over the upper and/or lowerteeth. The walls of the preformed tray may be either parallel or flared,the latter providing a larger top opening than the width of the traybottom. The tray advantageously includes a handle, preferably attachedat the front lower portion of the tray.

[0016] The tray or sheet is advantageously designed and formulated so asto soften when heated to a desired temperature above body temperature(i.e. 98.6° F.), preferably in a range of about 110° to about 180° F.,more preferably in a range of about 120° to about 170° F., and mostpreferably in a range of about 130° to about 160° F. Upon heating to anappropriate temperature at or above its softening temperature, the trayor sheet becomes plastically deformable and moldable so that it can forman impression of the teeth or teeth and gums.

[0017] The tray customization process is done by immersing the preformedtray or sheet into hot water or by other exposing it to other suitableheating means known in the art (e,g., heat gun, oven or torch). A handlecan be used to facilitate immersion of the tray in hot water or heatingusing other means while reducing the risk of burning one's fingers. Thetray or sheet will typically become plastically deformable after beingsubmerged within water heated to a temperature of about 160-212° F. orheated using other oppropriate heating means within a prescribed periodof time, preferably within about 1-30 seconds, more preferably withinabout 2-15 seconds, and most preferably within about 4-8 seconds.

[0018] When sufficiently softened and plastically deformable, the trayor sheet is placed over the person's upper and/or lower teeth and theperson closes his or her mouth. A vaccuum is advantageously createdinside the tray by the patient sucking in a manner so as to draw airand/or water out from the space between the tray and tooth surfaces.Additional forming pressure can be applied by the person's tongue or byplacing the patient's or dental practitioner's fingers against the outersurfaces of the tray. Nevertheless, due to the aforementioned benefit ofpreformed trays or sheets comprising ULDPE to shrink and cling againstand around the person's teeth when they begin to cool, less mechanicalforce is needed to cause the trays or sheets to adequately andaccurately conform to the person's teeth (or a stone model) compared toother tray materials known in the art.

[0019] As the tray remains in the person's mouth it begins to cool tobody temperature. After the customized tray has been formed and cooledsufficiently so that it is no longer plastically deformable, it isremoved from the person's mouth. The tray may be further cooled ifdesired, such as by placing the tray in cold water or by letting it aircool to room temperature. The formed tray will have an impression of theteeth and is therefore a “custom” or “customized” tray. Upon cooling,the tray may remain flexible and resilient but it will not be“plastically deformable” so as to assume a different restingconformation unless reheated and reshaped. If additional shaping isneeded, either immediately or later, the tray may be heated andcustomized as before.

[0020] Once the customization process is complete, the detachable handlecan be removed by e.g., cutting or tearing. The customized tray ispreferably trimmed to or shy of the gingival margin of the frontaland/or lingual surfaces. The tray is preferably scalloped in around theinterdental papilla in order to produce maximum customization andcomfort. Nevertheless, the tray can be trimmed to cover a portion of theteeth, just the teeth, or to cover a portion of the gingiva in additionto the teeth, as desired.

[0021] The customized trays formed in this manner are useful for toothbleaching or other dental treatments. Bleaching or other dentalcompositions can be applied to a person's teeth and/or gums by placingthe composition into the customized tray and placing the tray over theperson's teeth. The tray holds the dental composition against theperson's teeth and/or gums and keeps it from being diluted by saliva orotherwise being prematurely removed. In a preferred embodiment, thedental composition may include an appropriate tackifying agent in orderto make it sticky and viscous. The tray can be used once or many timesas desired to treat the person's teeth and/or gums.

[0022] In some cases, it may be desirable to incorporate reservoirswithin the customized tray. Reservoirs can enhance treatment of theteeth or other tissue by holding additional treatment material adjacentto the dental tissue(s) being treated. To form tray reservoirs, anappropriate blockout material, such as clay, wax, a light or chemicalcure resin, or other suitable coating material may be placed over one ormore of the person's teeth and/or gingival tissue. The blockout materialdisplaces the perform tray or sheet material away from the teeth by adistance corresponding to the thickness of the blockout material, whichresults in the creation of reservoirs within the customized tray. Aftertray formation, the blockout material is removed from the person's teethand/or gingival tissue.

[0023] Whereas preformed trays and sheets are especially useful formanufacturing customized dental trays using a person's teeth, ratherthan a stone cast, as the template, it is certainly within the scope ofthe invention to vacuum form preformed trays or sheets made from ULDPEusing a stone cast. An advantage of using preformed trays or sheets thatcomprise ULDPE using conventional tray-making methods that employ astone cast is that such trays or sheets, by virtue of their includingULDPE, can be made thinner than preformed trays or sheets usingconventional tray-making materials. In this way it is possible tomanufacture final customized trays that are even thinner walled and moreflexible than conventional trays. This is a surprising and unexpectedresult.

[0024] Moreover, ULDPE is more transparent or translucent thanconventional tray materials, which increases the ability to determinewhether the dental composition is sufficiently well distributed so as tocover the desired tooth and or gingival surfaces. This is yet anothersurprising and unexpected result of employing tray materials thatcomprise ULDPE.

[0025] These and other features of the present invention will becomemore fully apparent from the following description and appended claims,or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To further clarify the above and other advantages and features ofthe present invention, a more particular description of the inventionwill be rendered by references to specific embodiments thereof, whichare illustrated in the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope. The invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

[0027]FIG. 1 is a perspective view illustrating an embodiment of apreformed dental tray according to the invention that can be used toform a customize dental tray;

[0028]FIG. 2 is a perspective view illustrating a preformed sheet thatmay be used to form a customized dental tray according to the invention;

[0029]FIGS. 3A and 3B illustrate alternative methods of applying ablockout material to a person's teeth (or stone cast) in order to yielda customized dental tray having reservoirs;

[0030] FIGS. 4A-4C illustrates alternative methods of heating apreformed tray in order to soften it preparatory to making a customizeddental tray;

[0031]FIG. 5 illustrates the preformed dental tray of FIG. 1 beingplaced in a patient's mouth during formation of a custom-fitting trayusing a person's teeth as a template;

[0032]FIGS. 6A and 6B illustrate intermediate customized dental traysbeing trimmed in order to remove excess tray forming material; and

[0033]FIG. 7 illustrates a customized dental tray according to theinvention that has been trimmed and scalloped.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] In one aspect, the invention relates to the manufacture ofcustomized dental trays using a person's own teeth as the template. Inanother aspect, the invention relates to the use of preformed trays orsheets that comprise ULDPE in making customized dental trays, eitherusing a person's teeth or a stone cast of the person's teeth as atemplate. In another aspect, the invention relates to customized dentaltrays that comprises ULDPE. The inventive dental trays can be used forany desired dental treatment, such as tooth bleaching, fluoridetreatments, and antimicrobial treatments. Reference is now made to thedrawings.

[0035]FIG. 1 depicts a preformed dental tray 10 that may be used tomanufacture a customized dental tray according to the invention. Thepreformed tray 10 comprises a bottom wall 12 having a generally U-shapedconfiguration generally conforming to the shape of the person's dentalarch. The bottom wall 12 has a generally flat planar profile, althoughit could have other shapes if desired (e.g., curved). The preformed tray10 further includes a front side wall 14 and a rear side wall 16 that,together with the bottom wall 12, form a tray 10 that is open at the topand that terminates at ends 18. A detachable handle 20 is attached tothe tray 10 along an outer surface of the front side wall 14, preferablynear the bottom center of the side wall 14. The interface between thedetachable handle 20 and the front side wall 14 can be any desiredlength, preferably about 2-4 mm long, more preferably about ⅛ inch long(about 3.2 mm).

[0036] The front side wall 14 of the tray 10 is substantiallyperpendicular relative to the bottom wall 12. The rear side wall 16 ofthe tray 10 is substantially perpendicular to the bottom wall 12 at theends 18 of the horseshoe-shaped tray 10, but gradually opens up to forman oblique angle near a middle curved portion 22 of the tray so as tobetter accommodate the roof of the mouth near the middle portion 22 ofthe tray 10. The bottom wall 12 has a width near the curved middleportion 22 of the tray that is advantageously less than the width of thebottom wall 12 between the middle portion 22 and the ends 18 of the tray10. This allows for the differences in the radial width of a person'sincisors and canines relative to the bicuspids and molars. It should beunderstood, however, that dental trays comprising ULDPE used within thescope of the invention can have any desired configuration such that thetray of FIG. 1 is merely a nonlimiting example.

[0037] The tray 10 can be made of any appropriate thermoplastic materialthat is able to soften at a predetermined temperature greater than bodytemperature so as to become plastically deformable but that willmaintain its shape when cooled to at or below body temperature. Apreferred thermoplastic material is ultra low density polyethylene(ULDPE), which can be used alone or in combination with other polymers,such as polypropylene (PP), ethylene vinyl acetate (EVA),polycaprolactone (PCL), and other forms of polyethylene (PE). Flowadditives and plasticizers may be added as desired.

[0038] ULDPE is the preferred thermoplastic material because of itsability to maintain its structural form and integrity even after beingheated sufficiently so as to become plastically deformable. Though theybetter maintain their shape and size during the heating process,preformed trays and sheets provide the unexpected and surprising benefitof shrinking and clinging against and around the person's teeth (orstone model of the person's teeth) upon cooling. This greatly aids inthe ability and ease of tray materials comprising ULDPE to accuratelyand readily conform to the shape of the person's teeth (or stone model)compared to all (or virtually all) other tray materials known in theart. Moreover, customized trays that comprise ULDPE remain soft,flexible and resilient at room temperature. They are also moretransparent or translucent than conventional tray materials. ULDPEreduces or eliminates the toxicity concerns of EVA, while providingsuperior mechanical properties. ULDPE helps in the ease of manufactureof the customized dental tray and it also maximizes patient comfort andcompliance with the desired dental treatment.

[0039] ULDPE refers to a range of polyethylene-based copolymers definedas having a density of less than 0.914 g/cm³. By way of comparison, lowdensity polyethylene (LDPE) is defined as having a density in a range of0.915-0.94 g/cm³ and high density polyethylene (HDPE) is defined ashaving a density in a range of 0.94 to 0.97 g/cm³. Thus, ULDPE can bereadily distinguished from other forms of PE by its density, althoughits physical properties also differ significantly in many respects,including water vapor transmission rate, crystallinity, melting point,coefficient of linear expansion, elasticity, modulus, yield strength,tensile strength, hardness, and impact strength. In general, ULDPE is anethylene copolymer characterized as having excellent environmentalstress crack resistance, outstanding flex-life and flex-crackresistance, toughness and good sealability. It also has a relativelyhigh melt flow index compared to conventional tray materials, whichmakes it uniquely suitable for use in manufacturing thin-walledcustomized dental trays. It has been found that, in general, the higherthe melt flow index, the more the preformed trays or sheets made fromthe material will tend to maintain their shape after being heated to thematerial's softening temperature.

[0040] Examples of suitable ULDPE materials include various polymerssold under the general trade name Attane® by Dow Chemical. In general,Attane® refers to polyethylene copolymers made from ethylene and octene.Specific examples include Attane® 4201 (density=0.912 g/cm³), Attane®4202 (density=0.913 g/cm³), Attane® 4203 (density=0.905 g/cm³), Attane®4301 (density 0.914 g/cm³), and Attane® 4404 (density=0.904 g/cm³).Another suitable ULDPE material is Exact® 4041 (density=0.878 g/cm³)made by Exxon-Mobil Chemical. An example of a suitable EVA material isElvax® 250, available from Dupont. An example of a suitable PCL materialis Capra® 650 from Solvoy-Interox. Other thermoplastic materials andblends used in making dental trays are disclosed in U.S. Pat. No.5,769,633 to Jacobs et al., U.S. Pat. No. 5,051,476 to Uji et al., andU.S. Pat. No. 6,089,869 to Schwartz. For purposes of disclosingthermoplastic materials that can be made into customized dental trays,the foregoing patents are incorporated herein by reference.

[0041]FIG. 2 depicts a generally flat preformed sheet 24 that mayalternatively be used to form customized dental trays according to theinventive methods disclosed herein. The preformed sheet 24 preferablycomprises ULDPE, either alone or blended with one or more additionalpolymers. The preformed sheet 24 is preferably a square havingdimensions of about 5×5 inches, although other shapes and sizes arewithin the scope of the invention. For example, the preformed sheet maybe cut into a generally horse-shoe shaped configuration (not shown)generally corresponding to the size and curvature of a person's dentalarch.

[0042] In a preferred embodiment, the preformed tray 10 or sheet 24become plastically deformable at a predetermined temperature in a rangeof about of about 110° to about 180° F., more preferably in a range ofabout 120° to about 170° F., and most preferably in a range of about130° to about 160° F. The preformed tray 10 or sheet 24 preferablybecomes plastically deformable after being immersed in water attemperature of about 160-212° F. (or by heating using other appropriateheating means) within about 1-30 seconds, more preferably within about2-15 seconds, and most preferably within about 4-8 seconds.

[0043] The preformed tray 10 may advantageously be made available in avariety of sizes to accommodate varying sizes of teeth and/or dentalarches. This aids tray forming and customization because a preformedtray that more closely fits the patient's mouth and teeth size can beselected. The preformed sheet 24 may likewise come in various sizesalthough it is more amenable to tray-forming methods that employ “onesize fits all” approach than the preformed tray 10.

[0044]FIGS. 3A and 3B depict the optional use of a blockout material inorder to yield a finished customized tray incorporating one or morereservoirs therein. Reservoirs may be desirable in order to provideadditional dental composition adjacent to the teeth and/or gingivaltissue being treated. Once a customized tray has been formed and thenremoved from the person's teeth, the blockout material is removed.

[0045]FIG. 3A depicts the application of a flowable blockout material 30(e.g., a curable resin) onto the surfaces 32 of a person's teeth 34 (orstone cast) using a syringe tip 36 attached to a syringe (not shown). Asshown therein, the flowable blockout material 30 may be applied to so asto substantially cover the tooth surfaces 32 just shy of the gingivalmargin 38, although it is certainly within the scope to cover the entiretooth surface and/or at least a portion of the gingiva if desired (orthe portions of the stone cast representative of the person's toothsurfaces and gingival margin).

[0046]FIG. 3B depicts the application of a wax, clay or putty blockoutmaterial 40 by pressing it against the tooth surfaces (or stone cast)using a person's finger 42. Alternatively, highly viscous blockoutmaterials or clays may be applied and/or excess blockout material may beremoved using an application tool (not shown), such as a spatula.

[0047] The preformed tray 10 preferably has a composition and thicknessso that when it is heated so as to become plastically deformable, thetray will tend not to collapse but will substantially retain its shapeso that it can be readily molded into a customized dental tray. Thebenefit of using ULDPE is that ULDPE allows for the use of a thinnerpreformed tray or sheet compared to conventional tray materials.

[0048] In order to achieve the desired mechanical properties, both inthe preformed tray and in the finished customized tray, the bottom wall12 will preferably have a thickness of about 0.4 mm to about 2 mm, morepreferably in a range of about 0.6 mm to about 1.5 mm, and mostpreferably in a range of about 0.8 mm to about 1.3 mm. The front sidewall 14 and rear side wall 16 preferably have wall thicknesses in arange of about 0.3 mm to about 1.8 mm, more preferably in a range ofabout 0.4 mm to about 1.4 mm, and most preferably in a range of about0.7 mm to about 1.2 mm.

[0049] When using a preformed sheet to manufacture the customized dentaltrays according to the invention, the preformed sheet will preferablyhave a thickness of about 0.4 mm to about 2 mm, more preferably in arange of about 0.6 mm to about 1.5 mm, and most preferably in a range ofabout 0.8 mm to about 1.3 mm.

[0050] Reference is now made to FIGS. 4A-4C, which depict variousmethods for heating a preformed tray prior to forming the customizeddental tray. FIG. 4A depicts a preformed tray 10 immersed in a bath 50of hot or boiling water or other suitable liquid. The handle 20 allowsthe tray 10 to be submerged easily by the user and will advantageouslyremain outside the bath 50 as shown in FIG. 4A. This allows the tray 10to be easily removed from the bath 50 after being heated to the desiredtemperature. In the alternative, the handle 20 may be submerged in thebath 50 along with the tray 10 and then grasped using a pair of tonguesor other suitable gripping device (not shown) in order to remove thetray 10 from the bath 50.

[0051]FIG. 4B depicts the alternative use of a heat gun 52 to heat thepreformed dental dray 10. FIG. 4C depicts the alternative use of a torch54 to heat the preformed dental dray 10. When using these alternativeheat sources, care should be taken to heat the tray evenly, such as bymoving the tray and/or heat source back and forth to avoid heating asingle area to the exclusion of other areas.

[0052] Referring now to FIG. 5, after the tray 10 (or sheet 24, notshown) has been heated sufficiently so as to assume a plasticallydeformable condition, the tray 10 (or sheet 24, not shown) is insertedinto the mouth of a person 56 (e.g., a patient) over the upper or lowerteeth and the patient 56 closes his or her mouth. The preformed tray orsheet is plastically deformed (i.e., molded) so as to conform andcorrespond to at least a portion of the person's teeth. The person mayassist this process by sucking and creating a vacuum within the person'smouth. This causes any water and/or air interposed between the person'steeth and tray material to be removed so that the tray material can moreclosely conform to the shape of the person's teeth. Additional formingpressure can be applied by the fingers of the person or the fingers ofanother assisting in the formation of the customized tray. The personmay also use his or her tongue to press the tray material more closelyagainst the lingual tooth surfaces. Nevertheless, due to theaforementioned benefit of preformed trays or sheets comprising ULDPE toshrink and cling against and around the person's teeth when they beginto cool, less mechanical force is needed to cause the trays or sheets toadequately and accurately conform to the person's teeth (or a stonemodel) compared to other tray materials known in the art.

[0053] After the preformed tray 10 (or preformed sheet 24) has beenadapted so as to correspond to the person's teeth and has remained inthe person's mouth for a significant period of time, it will naturallybegin to cool. After the tray 10 (or sheet 24) has been customized so asto form an impression 58 within the intermediate customized tray 60(FIGS. 6A and 6B) and is no longer plastically deformable, it is takenout of the mouth. It may be further cooled as desired, such as byplacing the intermediate customized tray 60 in cold water or by lettingit cool to room temperature. When cooled sufficiently, the impression 58within the final customized tray 70 (FIG. 7) will become permanent. Thatis, the tray material can then be deformed to the extent that it isflexible and resilient but will return to its original customized shapeupon removal of the deformation force. If additional plastic deformationis needed, either immediately or later, the customized trays 60, 70 maybe heated so as to become plastically deformable, plastically deformed,and then cooled as describe above.

[0054] In the alternative, the intermediate customized tray 60 can bemade by vacuum forming a preformed sheet that comprises UDLPE usingconventional tray forming methods from a stone cast of a person's teeth.The preformed sheet 24 may be heated before or during vacuum formationas desired. The advantage of using a preformed sheet comprising UDLPE isthat the final customized tray made therefrom can be thinner, moreflexible, and more transparent compared to convention vacuum formeddental trays. It is also within the scope of the invention to form acustomized dental tray from a preformed tray comprising UDLPE using astone cast in order to obtain the same advantages.

[0055] In another embodiment, a preformed sheet 24 comprising ULDPE isplaced over the person's teeth with the assistance of an auxiliaryimpression of the person's teeth. First, an impression of the person'steeth (not shown) is made using any suitable impression material (e.g.,alginate or silicone). Second, the preformed sheet 24 is heated so as tobecome plastically deformable. Third, the heated preformed sheet 24 isplaced over the impression of the person's teeth. Fourth, the preformedsheet 24 is placed over the person's teeth with the assistance of theimpression in order to cause the sheet to conform to the person's teethand form a customized tray. The impression assists in causing thepreformed sheet to conform to the person's teeth.

[0056] Once the intermediate customized tray 60 has been formed usingthe preformed tray 10, the detachable handle 20 can be removed, such asby cutting or tearing. The customized trays 60, 70 may be sanded orotherwise smoothed in the area where the detachable handle 20 was cut orremoved so as to remove any points or edges that might cause discomfortto the patient.

[0057] As shown in FIGS. 6A and 6B, once formed, the intermediatecustomized tray 60 formed by whatever means can be trimmed as desired toyield a finished customized tray of a desired shape, such as to yieldthe finished tray 70 depicted in FIG. 7. In one embodiment, thecustomized dental tray can be trimmed so as to terminate at or shy ofthe gingival margin on both frontal and lingual surfaces. It may bedesirable to scallop or trim the customized dental tray up and aroundinterdental papilla so that the finished tray does not overlap them soas to achieve maximum patient comfort.

[0058] In general, the customized dental tray can be trimmed to cover aportion of the teeth, just the teeth, or to cover a portion of thegingival margin in addition to the teeth. In one embodiment, it may bedesirable to trim the customized dental tray so that enough traymaterial is left to assure that all of the tooth can be covered towithin about ¼ mm to about ⅓ mm of the gingival margin.

[0059] As shown generally in FIG. 7, the finished tray 70 comprises afront upper periphery 72 that overlaps a desired portion of the person'sfrontal tooth surfaces, and optionally at least a portion of thegingival, when in use. The dental tray also includes a rear upperperiphery 74 that overlaps a desired portion of the person's lingualtooth surfaces when in use. Together, the front upper periphery 72 andthe rear upper periphery 74 comprise the “upper periphery” of thecustomized dental tray. The finished tray 70 further also includes amain body portion 76 having an impression 78 formed therein.

[0060] The customized dental trays made according to the invention canhave any desired thickness. The customized trays wall preferably have anaverage wall thickness in a range of about 0.3 mm to about 1.8 mm, morepreferably in a range of about 0.4 mm to about 1.4 mm, and mostpreferably in a range of about 0.7 mm to about 1.2 mm.

[0061] The finished customized dental trays according to the inventionare useful for teeth bleaching or other dental treatments. In use, adesired dental composition is placed within the main body portion of thetray and the tray is placed over the person's teeth. The customized trayholds and maintains the dental composition against the person's teeth.The customized dental trays according to the invention can be used onceor repeatedly as desired. Transparent trays made using UDLPE or blendsthereof are both visually appealing and more practical in the sense thatit can be readily determined whether the person's teeth are adequatelyor evenly covered with the dental composition during treatment.

Comparative Study

[0062] A preformed dental tray similar to the tray depicted in FIG. 1was made from ULDPE. The tray had a front and rear side wall thicknessof 0.042 inch (1.08 mm) and a bottom wall thickness of 0.5 inch (1.27mm). A number of such trays were heated in baths of boiling water havingtemperatures that ranged between 160-212° F. for a time period rangingfrom 3 to 20 seconds. In all cases the trays maintained sufficientphysical integrity so that they could be successfully placed over aperson's teeth and formed into a customized tray. The finished trayswere soft, thin-walled, resilient, comfortable-fitting and virtuallytransparent.

[0063] By comparison, preformed trays made from EVA having a similarwall thickness were not able to maintain their physical integrity whenheated in a similar manner. Instead, such trays tended to shrink andcollapse in a manner that rendered them virtually useless. The front andrear side walls tended to collapse together, which made it virtuallyimpossible to place over a person's teeth. They also shrunk andshriveled in a manner that substantially altered their initial sizeprior to being placed over a person's teeth, thereby further renderingthem unsuitable for use in making a customized dental tray using aperson's own teeth as a template. Studies have shown that preformedtrays made from EVA must be significantly thicker-walled compared topreformed trays comprising ULDPE in order to perform with minimaladequacy. EVA trays having a wall thickness less than 1.5 mm have beenfound to be inadequate for formation of a customized dental tray using aperson's teeth as a template without the use of an external supportmember, such as the outer tray disclosed in U.S. Pat. No. 5,616,027 toJacobs et al. In general, EVA trays must typically have about twice thewall thickness as trays made from ULDPE in order to provide the samestructural integrity when heated. This is yet another surprising andunexpected benefit of using preformed dental trays that comprise ULDPE.

[0064] The present invention may be embodied in other specific formswithout departing from its spirit or essential characteristics. Thedescribed embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by the foregoingdescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

What is claimed is:
 1. A preformed tray for use in forming a customizeddental tray comprising ultra low density polyethylene, the preformedtray further comprising: a bottom wall having a substantially U-shapedconfiguration; a front side wall extending laterally from an outer edgeof the bottom wall; a rear side wall extending laterally from an inneredge of the bottom wall; and a hollow interior defined by the bottomwall, front side wall, and rear side wall that is sized and configuredso as to approximate a corresponding shape of a person's dental arch. 2.A preformed tray as defined in claim 1, the thermoplastic materialfurther comprising at least one of a low density polyethylene, ethylenevinyl acetate, polycaprolactone, polypropylene, or another type ofpolyethylene.
 3. A preformed tray as defined in claim 1, the bottom wallhaving a thickness in a range of about 0.4 mm to about 2 mm.
 4. Apreformed tray as defined in claim 1, the bottom wall having a thicknessin a range of about 0.6 mm to about 1.5 mm.
 5. A preformed tray asdefined in claim 1, the bottom wall having a thickness in a range ofabout 0.8 mm to about 1.3 mm.
 6. A preformed tray as defined in claim 1,the front and rear side walls each having a thickness in a range ofabout 0.3 mm to about 1.8 mm.
 7. A preformed tray as defined in claim 1,the front and rear side walls each having a thickness in a range ofabout 0.4 mm to about 1.4 mm.
 8. A preformed tray as defined in claim 1,the front and rear side walls each having a thickness in a range ofabout 0.7 mm to about 1.2 mm.
 9. A preformed tray as defined in claim 1,further comprising a handle attached to and extending laterally from asurface of the front side wall.
 10. A preformed tray as defined in claim1, the preformed dental tray being plastically deformable at atemperature in a range of about 110° to about 180° F.
 11. A preformedtray as defined in claim 1, the preformed dental tray being plasticallydeformable at a temperature in a range of about 120° to about 170° F.12. A preformed tray as defined in claim 1, the preformed dental traybeing plastically deformable at a temperature in a range of about 130°to about 160° F.
 13. A preformed tray as defined in claim 1, thepreformed dental tray being flexible and resilient below its softeningpoint.
 14. A preformed tray as defined in claim 1, the front side wallbeing substantially perpendicular to the bottom wall.
 15. A preformedtray as defined in claim 1, a portion of the rear side wallcorresponding to the location of the person's molars being substantiallyperpendicular to the bottom wall and a portion of the rear side wallcorresponding to the location of the person's incisors having an obliqueangle relative to the bottom wall.
 16. A preformed tray as defined inclaim 1, the bottom wall being substantially planar.
 17. A preformedtray as defined in claim 1, the bottom wall being curved.
 18. Apreformed tray as defined in claim 1, the preformed tray characterizedas substantially maintaining its initial size and shape when heated soas to become plastically deformable but shrinking so as to conform to aperson's teeth when placed over the teeth and allowed to cool.
 19. Apreformed tray for use in forming a customized dental tray comprising athermoplastic material that becomes plastically deformable attemperature in a range of about 110° to about 180° F., the preformedtray further comprising: a bottom wall having a substantially U-shapedconfiguration and a thickness in a range of about 0.8 mm to about 1.3mm; a front side wall extending laterally from an outer edge of thebottom wall and having a thickness in a range of about 0.7 mm to about1.2 mm; a rear side wall extending laterally from an inner edge of thebottom wall and having a thickness in a range of about 0.7 mm to about1.2 mm; a hollow interior defined by the bottom wall, front side wall,and rear side wall that is sized and configured and to approximate acorresponding shape of a person's dental arch; and a handle attached toand extending laterally from a surface of the front side wall.
 20. Apreformed tray as defined in claim 18, the handle and front side wall ofthe preformed tray having an attachment interface with a length of about2 mm to about 4 mm.
 21. A preformed tray as defined in claim 18, thepreformed tray comprising ultra low density polyethylene.
 22. Apreformed tray as defined in claim 18, the preformed tray maintainingsufficient integrity and avoiding collapse when plastically deformableso that it can be placed over a person's teeth without a supportingouter tray device.
 23. A preformed tray for use in forming a customizeddental tray comprising ultra low density polyethylene, the preformedtray further comprising: a bottom wall having a substantially U-shapedconfiguration and a thickness in a range of about 0.4 mm to about 2 mm;a front side wall extending laterally from an outer edge of the bottomwall and having a thickness in a range of about 0.3 mm to about 1.8 mm;a rear side wall extending laterally from an inner edge from the bottomwall and having a thickness in a range from about 0.3 mm to about 1.8mm; a hollow interior defined by the bottom wall, front side wall andrear side wall that is sized and configured so as to approximate acorresponding shape of a person's dental arch; and a handle attached toand extending laterally from a surface of the front side wall.
 24. Apreformed tray as defined in claim 23, the bottom wall having athickness in a range of about 0.6 mm to about 1.5 mm and the front andrear sidewalls each having a thickness in a range of about 0.4 mm toabout 1.4 mm.
 25. A preformed tray as defined in claim 23, the bottomwall having at thickness in a range from about 0.8 mm to about 1.3 mmand the front and the rear sidewalls each having a thickness in a rangeof about 0.7 mm to about 1.2 mm.
 26. A preformed tray as defined inclaim 18, the handle and front sidewall of the preformed tray having anattachment interface with a length of about ⅛ inch.